1. Field of the Invention
The present invention relates to a backlight inverter which is applied to a U-shaped lamp, and more particularly to a backlight inverter for a U-shaped lamp which is capable of detecting an abnormal state of an inverter circuit, such as an opened or shorted state of the inverter circuit and/or lamp, breaking or arcing of the lamp, or etc., and shutting down the inverter circuit upon detecting the abnormal state thereof, so as to enhance operational reliability thereof.
2. Description of the Related Art
A backlight inverter is generally adapted to convert a low direct current (DC) voltage into an alternating current (AC) voltage and reconvert the AC voltage into a high voltage using a transformer to light a lamp. Since the backlight inverter induces the high voltage in an output terminal thereof, it must be shut down upon being touched by a person, so as to inflict no bodily injury on the person. The inverter also has separate specifications on safety standards.
Lamps for backlighting can be roughly classified into a linear lamp which has been traditionally used and a U-shaped lamp, the use of which has gradually increased.
One example of a backlight inverter for a linear lamp will hereinafter be described with reference to FIG. 1.
FIG. 1 is a schematic view of a conventional backlight inverter for a linear lamp.
As shown in FIG. 1, the conventional backlight inverter for the linear lamp, denoted by reference numeral 10, a transformer driver 11 for converting an input DC voltage into an AC voltage in response to a control signal, a transformer 12 for boosting the AC voltage converted by the transformer driver 11 to a high voltage of about 1 to 2 kV required to drive the lamp and supplying the boosted high voltage to the lamp, a current detector 13 for detecting current Is flowing through the lamp, and a driver controller 14 for detecting a shorted or opened state of an output terminal of the inverter according to the current detected by the current detector 13 and controlling shutdown of the driver 11 upon detecting the shorted or opened state.
The current detector 13 includes a resistor R connected to a cold terminal of the lamp, and acts to detect current corresponding to a voltage across the resistor R.
This conventional backlight inverter is operated in the following manner. Under the condition that the lamp is normally connected, the lamp is normally lighted, the detected current is applied to the driver controller 14 and the output voltage of the inverter is constantly maintained.
However, when there occurs an abnormal state of the inverter such as an opened or shorted state of a hot or cold terminal of the lamp, the inverter is shut down. For example, in the case where the output terminal of the backlight inverter is opened, no current flows through the lamp, so the detected current Is becomes “0”. As a result, the driver controller shuts down the inverter.
On the other hand, in the case where the output terminal of the backlight inverter is shorted to ground, the detected current Is becomes “0” because the output terminal is connected to the ground. As a result, the driver controller shuts down the inverter.
In the conventional backlight inverter applied to the linear lamp, as mentioned above, the detected current Is becomes “0” in either the opened state or shorted state of the hot or cold terminal of the lamp, and the backlight inverter can be shut down by sensing the detected current Is.
Meanwhile, a U-shaped lamp is recently being researched and developed for application as a lamp for backlighting owing to the advantage of being superior in efficiency to the linear lamp.
Since the U-shaped lamp is about twice as long as the linear lamp, a drive voltage which is about twice as high as that for the linear lamp is required to drive the U-shaped lamp. For example, the drive voltage is about 1300V for a 17-inch linear lamp and about 2650V for a 17-inch U-shaped lamp.
In this connection, when a conventional backlight inverter using one transformer is applied to drive the U-shaped lamp, the transformer must have a high withstand voltage, thereby making it difficult to drive the U-shaped lamp using such one transformer.
Accordingly, two transformers must be used to drive the U-shaped lamp and, in order to stably operate the U-shaped lamp using such two transformers, there is a need for a new scheme for detection of inverter abnormal states different from that applied to the backlight inverter using one transformer.